This invention relates to magnetic imaging and more particularly, to method and apparatus for creating an improved latent image on a magnetizable member.
There has recently been introduced a magnetic imaging system which employs a latent magnetic image on a magnetizable member which can then be utilized for purposes such as electronic transmission or in a duplicating process by repetitive magnetic toning and transfer of the developed magnetic latent image. Such latent magnetic image is provided by any suitable magnetization procedure whereby a magnetized layer of marking materials is magnetized, such magnetism transferred imagewise to the magnetic substrate. Such a process is more fully described in U.S. Pat. No. 3,804,511 to Rait et al. Such a process requires the utilization of an original image, creating a duplicate of the original image in magnetizable marking material, magnetizing the magnetizable marking material, and then transferring the signal from the magnetized marking material to a magnetizable member.
In magnetic recording systems conventional to audio and visual recording systems, the magnetic signal is recovered by an electronic "reading" head which reconstructs the desired signal into an appropriate audio or visual electronic signal. These conventional systems depend upon recording the magnetic signals on magnetizable member in "tracks" which are separated from one another by spacings or "guard bands" of the magnetizable member surface bearing no magnetic signal. These "guard bands" are absolutely necessary so that the "reading" head can accurately reconstruct the desired magnetic signal from the "track" that it is reading without being affected by the fringing magnetic fields from adjacent tracks.
In an imaging system wherein the magnetic latent image is desirably rendered visible with magnetic toner, as opposed to the conventional audio and visual magnetic recording systems, the presence of "guard bands" are highly undesirable because magnetic toner is not attracted thereto. This phenomenon is detrimental to visible imaging schemes relying upon magnetic marking materials to develop a magnetic latent image since it leads to streaks or image deletions, especially in solid areas, upon development of the magnetic latent images.
Furthermore, amplitude modulated recording conventional to audio magnetic recording and disclosed in U.S. Pat. Nos. 3,013,124; 3,479,036 and 3,275,757 are not desirable for visible development of magnetic latent images. This is so because latent magnetic images for visible development is characterized by very high gamma and little or no "gray" scale can be obtained by using an amplitude varying signal. Accordingly, an amplitude modulated magnetic image would result in loss of good solid area coverage upon development with a magnetic marking material.
The present invention provides an improved magnetic latent image capable of being rendered visible with magnetic marking material without image deletion.